As a somatometry using light, an optical topography which is used for measuring brain function has been known as disclosed, for example, in Japanese Patent Publication Nos. JP-A-9-98972 and JP-A-5-115485. In such optical topography, light is illuminated on a living body representing a measurement object (a subject), and transmitted and scattered light from the tissue in vivo is collected and detected at a point remote from the illumination point by a few mm to a few cm. An optical fiber is generally used as a light guiding means when illuminating light onto a living body and detecting light from the living body. From the measured intensity of the transmitted and scattered light from the tissue in vivo a density of light absorption substance in vivo can be determined. As examples of such light absorption substances oxyhemoglobin and deoxyhemoglobin representing metabolic substances in vivo arc enumerated. When determining the density of a light absorption substances, the light absorption characteristics of the light absorption substance corresponding to the wavelength of the illuminate light are used. In general, when measuring a deep portion in a living body, a light having a wavelength in a range from 650 mm to 1300 mm is used which shows a high in vivo transmissivity.
FIG. 13 shows a conventional topographic image displayed on a display unit in an in vivo optical measurement device. A topographic image 1 representing a physical quantity of in vivo metabolic substance within a measurement region is shown in a window 2. The present image displays a distribution of measured amount or its variation of the in vivo metabolic substance which was obtained by illuminating a laser beam having a certain wavelength onto a tissue in vivo and by making use of the intensity of the transmitted and scattered light from the tissue in vivo and of the absorbance of the metabolic substance at the wavelength of the laser beam used. The interval between the laser beam illumination point and the detection point of the in vivo tissue transmitting light intensity, namely the interval between the measurement points is about a few cm which varies depending on the scattering characteristic of the tissue in vivo. Therefore, a measured amount or its variation of an in vivo metabolic substance at between measurement points is estimated by a statistical processing, for example, by interpolation.
In order to obtain detailed information on tissue in vivo a high spatial resolution is necessitated. However, a resolution of a present day in vivo optical measurement device is low and is about a few cm. Namely, when imaging a physical quantity of an in vivo metabolic substance, an imaging processing is performed through a statistical processing like a linear interpolation, however, a data at a point between measurement points can not be displayed and it was impossible to obtain a numerical information (a quantitative information) at the intermediate point. For this reason, it was difficult to obtain a detailed information of the in vivo tissue.